Deep-sea vent, hydrothermal (hot-water) vent formed on the ocean floor when seawater circulates through hot volcanic rocks, often located where new oceanic crust is being formed. Vents also occur on submarine volcanoes. In either case, the hot solution emerging into cold seawater precipitates mineral deposits that are rich in iron, copper, zinc, and other metals. Outflow of those heated waters probably accounts for 20 percent of Earth’s heat loss. Exotic biological communities are now known to exist around the vents; these ecosystems are totally independent of energy from the Sun, depending not on photosynthesis but rather on chemosynthesis by sulfur-fixing bacteria. Some of the world’s deepest hydrothermal vents occur at depths of roughly 5 km (3.1 miles) in the Cayman Trench, a submarine depression on the floor of the western Caribbean Sea.

Black smoker chimneys at the Vent 1 hydrothermal vent site on the southern cleft segment of the …

Major funding for this expedition was provided by NOAA Ocean Exploration Program and NOAA Vents Program; video clips edited by Bill Chadwick, Oregon State University/NOAA

A lush cluster of tube worms near a hydrothermal vent in the northeastern Pacific Ocean.

Major funding for this expedition was provided by NOAA Ocean Exploration Program and NOAA Vents Program; video clips edited by Bill Chadwick, Oregon State University/NOAA

An expedition seeking hydrothermal vents in the middle of the Atlantic Ocean.

University College Cork, Ireland (A Britannica Publishing Partner)

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...ecosystems. The existence of these life-forms in the deep ocean cannot be based on photosynthesis. Instead, they are nourished by minerals and heat. The energy released when hydrogen sulfide in the vent reacts with seawater is utilized by bacteria to convert inorganic carbon dioxide dissolved in seawater into organic compounds, a process known as chemosynthesis. Some scientists speculate that...

The most unusual biological communities of all are those surrounding hydrothermal vents on the ocean floor. These vents result from volcanic activity and the movement of continental plates that create cracks in the seafloor. Water seeps into the cracks, is heated by magma within Earth’s mantle, becomes laden with hydrogen sulfide, and then rises back to the ocean floor. Sulfur-oxidizing...

Producers were discovered in the aphotic zone when exploration of the deep sea by submarine became common in the 1970s. Deep-sea hydrothermal vents now are known to be relatively common in areas of tectonic activity (e.g., spreading ridges). The vents are a nonphotosynthetic source of organic carbon available to organisms. A diversity of deep-sea organisms including mussels, large bivalve...